Apparatus and method for folding synthetic plastic sheet stock



Aug. 24, 1965 c. E. PALMER 3,202,066

APPARATUS AND METHOD FOR FOLDING SYNTHETIC PLASTIC SHEET STOCK Filed 001;. 11, 1962 2 Sheets-Sheet 1 Z2 34 58 4a 6a 44 ,1 a 3% 4 i 4/ {4% 554 3% INVENTOR. 32 6 22 fig CHARLES E. PALMER 65 BY w ATTORNEY C. E. PALMER Aug. 24, 1965 APPARATUS AND METHOD FOR FOLDING SYNTHETIC PLASTIC SHEET STOCK 2 Sheets-Sheet 2 Filed Oct. 11, 1962 FIG. 8

FIG. 7

INVENTOR CHARLES E. PALMER ATTORNEY W United States Patent 3,2d2,%6 APPARATUS AND ME'IHGD FGR'FGLDKNG SYNTHETIC PLASTIQ SHEET STGEK Charles E. Palmer, Somers, (loam, assignor to Monsanto Company, St. Louis, Mix, a corporation of Delaware Filed Oct. 11, 1962, Ser. No. 229,937 9 Claims. (Cl. 93-49) The present invention relates to an improved method and appartus for folding synthetic plastic sheet stock.

In my United States Patent No. 2,954,725, issued October 4, 1960, and entitled Method and Apparatus for Folding Plastic Sheet Stock, there is disclosed a novel and highly effective method for folding synthetic plastic sheet stock by use of a rigid folding blade and a resilient, rubber-like die pad. In this method, the blank of plastic sheet material is depressed into the die pad material by movement of the folding blade relative thereto and the rubber-like material of the die pad flows to force the plastic sheet material about the edge of the blade and provide a sharp fold therein. In the method and apparatus disclosed in this patent, the blank is supported in a relatively stationary position with respect to movement laterally of the die pad member. A single die pad member of extensive lateral area or a plurality of individual die pad members are provided along the line or lines of fold and relative movement of the folding blade depresses the blank intothe die pad member or members. This method has proven highly advantageous in providing relatively high-speed and economical transparent packaging of various goods and in enabling use of various container designs and is currently enjoying extensive and increasing use.

It is an object of the present invention to provide a novel and accelerated method and apparatus for folding a blank of plastic sheet material wherein the blank moves laterally relative to the die pad and blade members to enable economical, high-speed folding adapted to use with extended lengths of plastic sheet material.

Another object is to provide an apparatus and method for such folding lengths of plastic sheet material which can beused in. combination with the method of my afore- ,mentioned,patent to provide economical, optimum operation at very high speeds.

Still another object is to provide a method and apparatus for folding extended lengths of tubular articles of polygonal section adapted for fabrication of containers.

Otherobjects and advantages will be apparent from the following detailed description and claims and the attached drawing whereinz.

FZGURE l is a perspective fragmentary view of apparatus for folding a generally V-shaped channel member;

FIGURE 2 is a fragmentary cross-sectional view along the line 2--2 of FIGURE 1 to an enlarged scale;

FIGURE 3 is a side elevational View of the mandrel and related elements in apparatus for forming a tubular member of general rectangular cross section with theplastic sheet stock shown in.phantom;

FIGURE 4 is a fragmentary cross-sectional view of the apparatus of FIGURE 3 with roller elements thereof omitted for clarity of illustration;

FIGURE 5 is a fragmentary perspective view of the tubular member formed by the apparatus of FIGURES 3 and 4;

FIGURE 6 is a fragmentary perspective View of an alternative embodiment of tubular member which may be formed in accordance with the present invention;

FIGURE 7 is a fragmentary cross section of another embodiment of folding blade and die pad members during the folding. operation;

FIGURE 8 is a fragmentary cross section. of still an- .ous container structures.

3,2d2,dd6 Patented Aug. 24, 1965 objects can be readily attained by providing a blade member of circular configuration with a blade edge extending about its periphery and a die pad memberof circular configuration with resilient, rubber-like material extending about its periphery which are rotatable in opposite directions with the blade edge extending into the rubberlike material, and passing the plastic sheet stock between the blade and die pad members as they rotate in opposite directions so that the blade edge of the blade member depresses the plastic stock into the rubber-like material of the die pad member sufficiently to cause the rubberlike material to flow and fold the stock. about the blade edge.

Although the blade and die pad members may be rotated about axes which deviate somewhat from parallel, optimum performance and quality of fold is obtained when substantially parallel axes are utilized. Depending upon the desired angle of fold in the plastic stock, the blade edge may extend radially of the die pad member or it may extend at an angle to the radius thereof; similarly, the outer periphery of the die pad member into which the foldingblade edge extends may be normal to the radius thereof or there may be a downwardly inclined face cooperating with the blade edge.

The die pad and blade members are driven by motor means and synchronized so that they have a substantially equal tangential speed at their area of engagement with the plastic stock to limit and prevent substantially any slippage of the plastic stock .therebetween and possible injury thereto due to concentration of excessive stresses or pressures at any point. Although the die pad and blade members may be disengaged toposition the plastic stock therebetween, optimum speed of operation is obtained by feeding the plastic sheet stock into the nip between them asthey rotate in engagement.

By providing a pluralityof pairs. of die pad and blade members, various forms may be folded from the plastic sheet stock including U-shaped channels for subsequent end folding operations and tubular articles having polygonal sections such as rectangular or triangular for vari- In order to prevent undue stress upon the stock at any point. and advancethe stock uniformly through the several pairs of folding members,

the rotational speed of each of several pairs of members should be synchronized so as to provide substantially equaltangential speeds at their area of engagement with the plastic stock. When multiple folds are made simultaneously using peripheral blade edges of substantially V-shaped section, the plastic material must be bowed or bellied between laterally spaced adjacent pairs of rotating members to provide sufiicient slack between the blades to enable the plastic material to deflect sufficiently about the blade edges during the folding operation. When the blade edge is located along the side edge of the blade periphery, the plastic material must be limited in its movement relative to the other side edgeeither by use of another pair of folding members or by auxiliary limiting means.

Generally, the plastic sheet stock must be folded to an angle greater than the desired angle of fold in the finished article. Thus, for. an angleof'90 degrees in the finished folding blade members 8,

' some deviation from parallel axes of rotation bodiment of the present invention for making a single fold in plastic sheet stock generally designated by the numeral 2. Rotatably carried by the shafts 4, 6 are the die pad member 8 and folding blade member 10, re spectively, which are of generally circular configuration.

V The die pad member 8 has a relatively rigid body portion 12 which is mounted upon the shaft 4 and a peripheral portion 14 of resilient, rubber-like material. The folding blade member Ill of this embodiment has a relatively thin body portion 16 which is reinforced by the shank 13 for stable mounting upon the shaft 6 and has a blade edge portion 20 of general V-shaped cross section extending about the periphery thereof.

In their illustrated operative position, the die pad and are supported for rotation with the blade edge portion 26 extending into the peripheral portion 14 of the rubber-like material. Although for members 8, 10 may be possible with different configurations of blade edges and die pad peripheral portions, parallel axes are highly preferable to obtain optimum control, sharpness of fold and efficiency.

In this illustrated embodiment, the die pad and folding blade members 8, 10 are driven in opposite directions and synchronously to provide substantially equal tangential speeds at their area of engagement by the drive shaft 22 and its pinion 24 which meshes with the large gear 26 on the shaft 4 of the die pad member 8 and with the small gear 28 which is mounted on the shaft 30 and in turn meshes with and drives the large gear 32 on the shaft 6 of the folding blade member 10. A linkage (not shown) is conveniently provided to separate the members f5, 10 and move them into an inoperative position during non-use so as to reduce wear on the rubber-like material of the die pad portion 14.

As the plastic sheet stock 2 is fed into the nip between the engaged'folding blade and die pad members 8, Ill in their operative position shown in FIGURES 1 and 2, the rotating members draw the plastic sheet stock therebetween and therethrough. The blade edge portion of the folding blade 10 presses the plastic sheet stock 2 into the resilient rubber-like material of the die pad member peripheral portion 14 sufiiciently to cause the rubberlike material to fiow and fold the plastic stock 2 about the blade edge portion 20 and along the side faces thereof. As the plastic sheet stock 2 emerges from between the members 8, 10, there occurs some relaxation or opening of the angle of fold in the plastic sheet stock determined by the included angle of the V-shaped blade edge portion 20 due to the inherent characteristics of the plastic material so that the blade edge portion 20 must be dimensioned'and configured to overfold the plastic stock sulficiently to achieve the desired angle of fold in the plastic stock upon relaxation of the folding pressure.

In FIGURES 3 and 4, there is illustrated an alternative embodiment of the invention for making a plurality of folds to form the plastic sheet stock 34- into a tubular form of generally rectangular cross section designated by the numeral 36 in FIGURE 5. In this embodiment, spaced about a central axis are four pairs of die pad members 38a, 38b, 38c, 38d and blade members 40a, 40b, 40c,

40d. In the illustrated embodiment, the several folding blade members 40 are rotatably supported on shafts 41 in an elongated folding mandrel 42 so that the blade edge portions 44 thereof extend outwardly of apertures in the apices of the generally star-shaped body portion 46 of the mandrel 42. As best seen in FIGURE 4, two of the blade members 40a, 40b are spaced laterally apart at the bottom of the mandrel 42 to make the center folds in the plastic sheet stock 34 and the remaining two blade members 400,406! are spaced longitudinally and upwardly therefrom on opposite sides of the mandrel to provide the outer folds in the plastic sheet stock.

In the illustrated embodiment, the several blade members 40' are driven synchronously in the same direction of rotation to have substantially equal tangential speeds by the drive shafts 48, 5d. The drive pinion 52 on the forward drive shaft 43 meshes with the gear 54:: on the shaft 41a of the folding blade member 40a and with the idler gear 56 which in turn meshes with the gear 54b on the shaft 41b of the folding blade member 40b. Similarly, the large drive pinion 58 on the drive shaft 58 meshes with the gear 54d of the folding blade member 40d and with the idler gear 663 which in turn meshes with the gear 542 of the folding blade member 540.

The four die pad members 38 are rotatably supported upon shafts 62 mounted in the support arms 64. In the illustrated operative position, the die pad members 38 are in engagement with the folding blade members 40 and the blade edge portions 44 thereof extend into the die pad member peripheral portions 66 of resilient, rubher-like material. Also, in the operative position, the die pad members 38 have their axes of rotation substantially parallel to the axes of rotation of their cooperating folding blade members 44 and are driven synchronously in a direction of rotation opposite thereto at substantially equal tangential speeds at their area of engagement so as to limit or prevent substantially any slippage and thus move the plastic sheet stock 34 smoothly therebetween. The drive pinion 68 on the drive shaft 70 meshes with the small gear 72 on the shaft 62 of the die pad member 38a and the bevel gear 74a thereon meshes with the bevel gear 74b on the shaft 62 of the die pad member 3815.

As seen in FIGURE 3, the plastic sheet stock 34 is fed from the right hand side of the mandrel 42 and rollers 76 aligned with the centerline of the mandrel deflect or bow the plastic sheet stock slightly upwardly into the recessed portion of the body portion 46 of the mandrel between the apices before it enters the nips between the folding blade members 44M, 4% and die pad members 38a, 38b to provide slack between the nips and allow the deflection necessary during folding about the U-shaped folding blade edge portions 44. After passage through this first set of folding members, the plastic sheet stock 34 assumes a generally U-shaped form and is guided into the nip of the second set of folding members 38c, 38d and 4ilc, 40d by guide rollers 30. The deflecting rollers 82 similarly provide slack in the sides of the plastic sheet stock before it enters the nip between this set of folding members. Upon passage beyond the folding mandrel 42, the folded stock assumes the tubular form of generally rectangular cross section shown in FIGURE 5. To reduce wear on the resilient rubber-like material, linkages (not shown) are desirably provided to disengage the blade to the angle included therebetween to edge portions therefrom and move them to an inoperative position. I

By use of three sets of folding members, the tubular form of triangular cross section designated by the numeral 84 in FIGURE 6 may be provided. tubular polygonal forms may be provided by proper spacing and dimensioning of the several sets of folding members.

In FIGURES 7-9, there are illustrated alternative designs for the folding members. In FIGURE 7, the folding blade member 86 has an undercut or hollowed side face portion designated by the numeral 88 adjacent the blade edge 90. As best seen in FIGURE 9, the die pad member has a body portion 94 and a peripheral portion 92 of resilient, rubber-like material which has a downwardly inclined side face 96 into which the periphery of the folding blade member 86 extends as seen in FIG- URE 7. The deformation and flow of the rubber-like material folds the plastic sheet stock 98 about the blade edge into the undercut side face portion 88 of the folding blade member 86 and along the other side face thereof produce overfolding of the plastic sheet stock. The plastic sheet stock is prevented from folding about the opposite side edge by being limited in its vertical displacement by a second set of Similarly, other folding members (not shown) or other convenient means such as a guide roller (not shown).

In FIGURE 8, the folding blade member 100 has a peripheral blade edge 102 provided by a separate member of generally frusto-conical configuration which seats in a circumferential recess in the periphery of the body portion 104. The plastic sheet 166 is overfolded about the side faces of the blade edge 162 to the angle included therebetween to produce the desired overfolding but is prevented from folding about the opposite edge of the member by limitation of its vertical displacement as in the case of the embodiment of FIGURE 7.

In the illustrated embodiments, the drive mechanism for the folding members (or the illustrated portion thereof) utilizes gear assemblies for delivering the power to the several members and for imparting synchronous rotation to obtain substantially equal tangential speeds at their area of engagement, thus minimizing or preventing slippage and injury to the plastic sheet stock. As will be readily appreciated, other means for imparting the desired synchronous movement to the folding members of a pair or of the several pairs can be provided by a plurality of synchronized motors connected directly to the several shafts supporting the folding members or by various arrangements and combinations of synchronized motors, belts and pulleys, gear transfer assemblies, and mechanical and fluid clutch mechanisms.

The various tubular forms such as the rectangular and triangular forms shown in FIGURES 5 and 6, respectively, are folded with overlapping portions which may be joined by mechanical locks such as shown in my United States Patent No. 3,019,957, issued February 6, 1962, and entitled Interlocking Engagement for a Plastic Blank, or by adhesive or heat sealing. Caps may be placed on the ends thereof to provide end closures or the tubular forms may have incised end portions which are further folded to provide integral locked end closures.

The present invention is particularly advantageous in combination with the method and apparatus of my aforementioned United States Patent No. 2,954,725 for use in folding trays such as shown in my United States Patent No. 2,967,654, issued January 10, 1961, and entitled Plastic Container Blank, by using a pair of spaced rotating folding members of the present invention to make the longitudinal folds forming a U-shaped channel in the first station of folding apparatus and subsequently making the end wall folds and locks in plunger-type apparatus of the type disclosed in my aforementioned earlier patent. In this manner, a large amount of running length of blank can be folded at great speeds and quickly fed to and positioned in the plunger-type apparatus.

The rubber-like material used for the die pad members may be any resiliently deformable and fiowable material such as sponge rubber and synthetic organic polymers such as polyurethanes. The rubber-like material may be secured to a rigid body element by adhesives or mechanically.

The present invention may be used in folding various synthetic plastic sheet materials which are capable of taking and substantially retaining a fold. In particular, biaxially oriented sheet materials of about 3 to 20 mils thickness are most advantageously employed because of the highly stressed nature of the sheet and its relative rigidity in thinner sheets. Biaxially oriented polystyrene of 5 to 13 mils thickness has proven particularly effective because of its relatively low cost commensurate with high strength and good clarity coupled with excellent ability to take and retain a fold. Generally, such material is overfolded about 20 to 40 degrees to achieve the desired set, folding to an angle of about 120 degrees being optimum to give rise to a stable 90 degree fold upon removal of the folding pressure due to the inherent relax characteristic in the sheet.

Thus, it can be seen that the method and apparatus of the present invention enable highly rapid and relatively economical cold folding of plastic sheet stock in both short and extended lengths. It can be used to fold tubular articles of polygonal cross section at rapid speeds for subsequent folding operations or for use with caps to provide containers, or it can be used to form channel-shaped members which are subsequently folded into tray or other container forms.

Having thus described the invention, I claim:

1. In the method of folding plastic sheet stock, the steps comprising providing two spaced pairs of folding members, said members of each pair being of generally circular configuration and having substantially parallel axes of rotation in operative position, one of said members of each pair being a die pad member having a resilient rubber-like material extending about its periphery and the other being a folding blade member having a blade edge extending about its periphery, said resilient rubber-like material of said die pad members having opposing side faces tapering outwardly and oppositely towards their circumferential edges, said blade members having peripheral portions of generally U-shaped cross-section with said blade edges being at the intersection of the circumferential face and the outer side face of said blade members defining said U-shaped cross-section; said blade edges of said pair of blade members extending into said rubber-like material of the cooperating die pad members at said tapering side faces thereof in operative position; rotating said members at substantially equal tangential speeds at their area of engagement with the folding blade and die pad members rotating in opposite directions; and passing a length of synthetic plastic sheet stock between said pairs of members, the blade edges of said rotating folding blade members depressing said stock into said tapering side faces of said resilient rubber-like material of the cooperating rotating die pad members sufficiently to cause said rubber like material to flow and fold said stock against said outer side face and along said circumferential face of said blade edges, said plastic sheet stock extending relatively tautly between said two pairs of folding members.

2. The method of claim 1 wherein the plastic sheet stock is biaxially oriented synthetic plastic.

3. The method of claim 1 wherein the plastic sheet stock is biaxially oriented polystyrene of about 5 to 15 mils thickness.

4. In the method of folding plastic sheet stock, the steps comprising providing two spaced pairs of folding members, said members of each pair being of generally circular configuration and having substantially parallel axes of rotation in operative position, one of said members of each pair being a die pad member having a resilient rubber-like material extending about its periphery and the other being a folding blade member having a blade edge extending about its periphery, said blade members having peripheral portions of generally V-shaped crosssection with said blade edges being at the intersection 'of the converging side faces of :said blade members defining said V-shaped cross-section; the blade edges of said pair of blade members extending into said rubber-like material of the cooperating die pad members in operative position; bowing a length of plastic sheet stock between the intended fold lines and in the direction of said blade members; rotating said members at substantially equal tangential speeds at their area of engagement with the folding blade and die pad members rotating in opposite directions; and passing said bowed length of synthetic plastic sheet stock between said pairs of members, the blade edges of said rotating folding blade members depressing said stock into said resilient rubber-like material of the cooperating rotating die pad members sufficiently to cause said rubber-like material to flow and fold said stock against said converging side faces of said blade edges, said plastic sheet stock bowing in the direction of '2' said blade members between said two pairs of folding members.

5. The method of claim 4 wherein the plastic sheet is biaxially oriented synthetic plastic.

6. The method of claim 4 wherein the plastic sheet stock is biaxially oriented polystyrene of about 5 to 15 mils thickness.

7. In apparatus for folding plastic sheet stock, the combination comprising two laterally spaced pairs of folding members of generally circular configuration, one of said members of each pair being a folding blade member having a blade edge extending about the periphery thereof, said blade member having a peripheral portion of generally U-shaped cross-section with said blade edge being at the intersection of the circumferential face and the outer side face defining said U-shaped cross-section, the other of said members of each pair being a die pad member having resilient rubber-like material extending about its periphery; support means rotatably mounting said blade and die pad members, said resilient rubber-like material of said spaced die pad members having opposing side faces tapering outwardly and oppositely towards their circumferential edges, said support means providing an operative position for said pairs of members wherein said blade edges of said blade members extend into said rubber-like material of the cooperating die pad members at said tapering side faces thereof; and means for rotating said members in opposite directions to impart substantially equal tangential speed to said pairs of members at their area of engagement in operative position.

8. The combination of claim 7 wherein said outer side face of said peripheral portion of said blade member is concave and the circumferential face is substantially parallel to the axis of rotation.

9. In apparatus for folding plastic sheet stock, the combination comprising two laterally spaced pairs of cooperating folding members of generally circular configuration, one of said members of each pair being a folding blade member having a blade edge extending about the periphery thereof, said blade member having a peripheral portion of generally V-shaped cross-section with said blade edge being at the intersection of the converging side faces defining said V-shaped cross-section, the other of said mem bers of each pair being a die pad member having resilient rubber-like material extending about its periphery; support means rotatably mounting said blade and die pad members, said support means providing an operative position for said members wherein said blade edges of said blade members extend into said rubber-like material of the cooperating die pad members; means for rotating said members in opposite directions to impart substantially equal tangential speed to said pairs of members at their area of engagement in operative position; and means for bowing plastic sheet stock between said two pairs of folding members and in the direction of said folding blade members.

References Cited by the Examiner UNITED STATES PATENTS 2,061,286 11/36 Millet 93-84 X 2,440,113 4/48 Noecker 93-84 X 2,661,947 12/53 Reynolds 9358 X 2,954,725 10/60 Palmer 93-51 FOREIGN PATENTS 366,814 1/39 Italy.

FRANK E. BAILEY, Primary Examiner. 

1. IN THE METHOD OF FOLDING PLASTIC SHEET STOCK, THE STEPS COMPRISING PROVIDING TWO SPACED PAIRS OF FOLDING MEMBERS, SAID MEMBERS OF EACH PAIR BEING OF GENERALLY CIRCULAR CONFIGURATION AND HAVING SUBSTANTIALLY PARALLEL AXES OF ROTATION IN OPERATIVE POSITION, ONE OF SAID MEMBERS OF EACH PAIR BEING A DIE PAD MEMBER HAVING A RESILIENT RUBBER-LIKE MATERIAL EXTENDING ABOUT ITS PERIPHERY AND THE OTHER BEING A FOLDING BLADE MEMBER HAVING A BLADE EDGE EXTENDING ABOUT ITS PERIPHERY, SAID RESILIENT RUBBER-LIKE MATERIAL OF SAID DIE PAD MEMBERS HAVING OPPOSING SIDE FACES TAPERING OUTWARDLY AND OPPOSITELY TOWARDS THEIR CIRCUMFERENTIAL EDGES, SAID BLADE MEMBERS HAVING PERIPHERAL PORTIONS OF GENERALLY U-SHAPED CROSS-SECTION WITH SAID BLADE EDGES BEING AT THE INTERSECTION OF THE CIRCUMFERENTIAL FACE AND THE OUTER SIDE FACE OF SAID BLADE MEMBERS DEFINING SAID U-SHAPED CROSS-SECTION; SAID BLADE EDGES OF SAID PAIR OF BLADE MEMBERS EXTENDING INTO SAID RUBBER-LIKE MATERIAL OF THE COOPERATING DIE PAD MEMBERS AT SAID TAPERING SIDE FACES THEREOF IN OPERATIVE POSITION; ROTATING SAID MEMBERS AT SUBSTANTIALLY EQUAL TANGENTIAL SPEEDS AT THEIR AREA OF ENGAGEMENT WITH THE FOLDING BLADE AND DIE PAD MEMBERS ROTATING IN OPPOSITE DIRECTIONS; AND PASSING A LENGTH OF SYNTHETIC PLASTIC SHEET STOCK BETWEEN SAID PAIRS OF MEMBERS, THE BLADE EDGES OF SAID ROTATING FOLDING BLADE MEMBERS DEPRESSING SAID STOCK INTO SAID TAPERING SIDE FACES OF SAID RESILIENT RUBBER-LIKE MATERIAL OF THE COOPERATING ROTATING DIE PAD MEMBERS SUFFICIENTLY TO CAUSE SAID RUBBER-LIKE MATERIAL TO FLOW AND FOLD SAID STOCK AGAINST SAID OUTER SIDE FACE AND ALONG SAID CIRCUMFERENTIAL FACE OF SAID BLADE EDGES, SAID PLASTIC SHEET STOCK EXTENDING RELATIVELY TAUTLY BETWEEN SAID TWO PAIRS OF FOLDING MEMBERS. 